Controllable fission of droplets and bubbles by pneumatic valve

We report a feasible method that can precisely control the fission of droplets by modulating the flow resistance using pneumatic valves. Multilayer soft lithography was used to fabricate the valves. They can be used as variable microfluidic resistor (VMR) to dramatically change the flow resistance. A simulation has been done to forecast the behavior of droplets. We used this technique to control break-up of generated droplets and direct their motion. Droplets with different volume ratios were obtained in one chip. To investigate the mechanism, an equivalent electrical circuit was introduced to compare with the fluid network. This method could potentially be applied to different geometries, especially for the microfluidic network consisting of a set of two parallel channels with a common inlet and different outlets in bifurcating channels. Besides, manipulation of bubbles was also demonstrated.